Summary

State of the Art: A partly well working method to thin surplus flowers in spring is the rope machine. However with older trees it doesn’t work sufficiently in the inner parts of the tree. Also the device must be used very softly in order to prevent physical and physiological damages to the trees. Definition of the problem: In several countries organic apple growers can use lime sulphur for flower thinning to regulate the crop load on the apple trees. In Switzerland, however, no spray product is allowed for early crop load regulation to control bi-annual bearing in organic apple growing. This is a key problem for organic apple growers in terms of high labour costs for manual thinning and in terms of high difficulties to achieve good quality fruit every year. Target group: Organic apple growers Methodology: On-Farm trials. Partly, e.g. to check phytotoxic effects in advance, also greenhouse experiments. We are testing different molasse and oil products using not-thinned, rope-thinned and lime-sulphur-thinned treatments as reference standards. Results, conclusion, state of the art: We found good thinning potentials with molasses (vinasse) products and emulgated oils. However, still a lot of optimizations need to be investigated.